I think probably about 30-40% of the population would be able to make adequate life decisions and control the use of drugs to the point where it would be recreational use only, and they would otherwise be able to live a productive and positive life.
But what about the other 60%? The majority of the public make bad long term decisions in order to get a quick payoff, examples: Payday loan companies, Fast food / obesity, binge drinking, credit cards .. these are (not absolute) but examples of how people "just cant wait" for the long term payoff and take 'fix' and run.
Having > 50% of the population addicted to drugs would be disastrous.
And another point: What of the health costs of all of these consenting adults? Here in the UK, public health care is free though the NHS - should society as a whole bare the cost of the drug addicted and unproductive majority?
I do actually think legalisation is the answer, but I'm not sure how to answer these tough questions first ...
Maybe drugs should be legal but very expensive?
What do you think?